Despite the views of some church leaders - such as George Pell - who deny global warming, most Christians understand the need to care for the natural world and have embraced the scientific consensus on global warming.

The Eastern Orthodox Patriarch Bartholomew I is known as the “green patriarch” and Popes Francis and Benedict XVI have regularly called for care for the world. Many Catholic bishops’ conferences and Protestant churches have also taken up the challenge.

But there is one thing that stymies Christians regarding the ecological crisis: they find it almost impossible to confront the issue of population.

Perhaps this is because we have never been in this situation before. All our previous ethical and theological norms don’t apply to the population catastrophe facing us. It involves radical rethinking of our oldest and most treasured moral presuppositions.

What needs to be rethought? First we have to jettison anthropocentrism, the focus on humankind and its needs to the exclusion of all other species and priorities.

Anthropocentrism rest on the assumption that we constitute the entire meaning of the cosmos. Priest and ecotheologian Thomas Berry says it is rooted in “our failure to think of ourselves as a species, interconnected with and biologically interdependent on the rest of reality.” We have become besotted with “the pathos of the human” and take ourselves and needs as the focus, norm, and arbiter of all that exists.

Anthropocentrism also leads straight to the absurd assumption that the entire world can be turned into a feed lot for humankind with loss of all wildernesses and the extinction of tens of thousands of species.

Linked to anthropocentrism is the secular myth of progress, the notion of infinite development whereby limitless human advancement is possible and desirable. In the 19th century this notion was promoted through universal popular education and the notion that evolution was always toward more complex and developed realities. Nowadays the myth of progress has been transmuted into economic terms with neo-rationalism’s concept of a perfect, infinite, ever-growing market, a pseudo-religion if ever there was one.

So what are we to do?

First we need to jettison the old anthropocentric cosmology. We now live in a limitless cosmos, both spatially and temporally. In this context theology and ethics must embrace the concept that it is absurd to say that humankind constitutes the entire meaning of this cosmos.

Our continuing existence is contingent on our recognition that we are a mere blip in cosmic time and space whose existence depends entirely on the rest of creation. We need the humility to recognize we are merely contingent creatures that have been blessed (or cursed?) with an excess of self-awareness.

Our lives are not purposeless, but our meaning is linked intimately to the whole cosmos. Saint Paul’s apocalyptic theology sees the whole cosmos “groaning inwardly” until it reaches its fulfilment. For Paul both the cosmos and humanity are caught-up in a process that will lead to “the redemption of matter” – the Greek word Sarx here can mean both “body” and “matter” - and he envisions a time when the whole material cosmos will reach fulfilment.

This vision of the value of matter must become a reality at the practical level.

The moral principle that flows from this is that matter in all its species manifestations has such value that it is destined for transcendent fulfilment. This principle lays extraordinary moral responsibilities upon us.

If, theologically, the entire cosmos is redolent of the divine, for us to destroy other species and to tear the world apart with our ever-escalating numbers and greediness involves us in an actual destruction of the image of the transcendent – what might be called a kind of “deicide”, killing God.

Remember here that all theology is a kind of metaphor. So you don’t have to agree with my theology to understand that a metaphor or symbol like this can be powerfully used to shift ethical attitudes toward more responsible fertility.

Paul Collins is speaking at the Fenner Conference on Environment: “Population, Resources and Climate Change - implications for Australia’s near future” at the Shine Dome, Canberra on October 10 and 11.